The great difficulty processing speech in noise is one of the most characteristic and devastating aspects of the sensory deficit of hearing loss in aging (presbycusis). Conventional binaural hearing aids do not satisfactorily solve this problem. The long-term goal of this project, therefore, will be to develop a better hearing aid. To do this the following specific aims are proposed: 1) Test the hypothesis that the principle of exaggerated dominance in bilateral asymmetric systems is applicable to the auditory domain. (our preliminary pilot data support this hypothesis,)The aim is to rebalance the perceptual inputs (intensity and interaural delay time across frequencies). 2) Measure the interaural delay time (IDT) with respect to frequency. 3) Investigate the interaction of loudness balance and IDT variations. 4) Design and fabricate a hearing aid using the principle of restored perceptual balances. 5) Comparatively test such a hearing aid for its improvement of speech perception under various environmental noise conditions. According to the model, the simultaneous balance of both intensity and IDT parameters is necessary for adequate correction, and may explain the recognized inadequacies of conventional aids. Complex waveform stimuli in the manner of Henning (1974) will be used to measure IDT variations with frequency and the interaction that exists between intensity and IDT with midline lateralization as an endpoint. These values will be used to set the intensity and delay parameters of a binaural hearing aid using 15 1/3 octave bandpass filters, each followed by a separate attenuator and adjustable time delay integrated circuit. Speech perception in noise will be measured for 40 subjects with sensorineural hearing loss in 6 conditions: unaided, with conventional amplification, with correction for loudness balance, with correction for IDT, all with and without loudness balance across the frequency spectrum. The importance of this research lies in helping people with hearing loss better understand speech, particularly in a noisy, conversational situation.